Abstract

Collective animal behaviour has attracted much attention recently, but cause-and-effect within interaction sequences has often been difficult to establish. To tackle this problem, we constructed a robotic fish (‘Robofish’) with which three-spined sticklebacks (Gasterosteus aculeatus L.) interact. Robofish is a computer-controlled replica stickleback that can be programmed to move around a tank. First, we demonstrated the functioning of the method: that the sticklebacks interacted with Robofish. We examined two types of interaction: recruitment and leadership. We found that Robofish could recruit a single fish from a refuge and could initiate a turn in singletons and in groups of ten, i.e. act as a leader. We also showed that the influence of Robofish diminished after the first 30 min that fish spent in a new environment. Second, using this method, we investigated the effects of metric and topological inter-individual distance on the influence that Robofish had on the orientation of fish in a shoal of ten. We found that inter-individual interactions during this turn were predominantly mediated by topological, rather than metric, distance. Finally, we discussed the potential of this novel method and the importance of our findings for the study of collective animal behaviour.

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Video of a Robofish experiment (plan view) in the test tank (width × length × depth 86 × 81 × 5 cm). Before the start of the trial, we placed ten three-spined sticklebacks and a robotic fish: ‘Robofish’, in the enclosed refuge (upper right corner of the tank on the video), and left them for 2 min. At the start of the trial (and after 2.5 s on the video), one wall of the refuge was raised remotely by fishing line. Robofish was then activated (after 4 s on the video) and moved along a standardised route and can be identified from sticklebacks as it is the first fish to move its entire body from beneath the refuge (judged from the viewpoint of the camera). Soon after Robofish made the first of its 90° turns, the sticklebacks made a sharp turn towards the lower side of the tank. The trial was stopped when Robofish had returned to the refuge. (MPG 3580 kb)